For playback of optical recording media it is important to determine the type of the optical recording medium. In general there are different media types. A possible classification is: CD (Compact Disk), CD-R(W) (Compact Disk Recordable/Rewritable), DVD-ROM (Digital Versatile Disk Read-Only Memory), DVD-R(W) (Digital Versatile Disk-Recordable/Rewritable), DVD+R(W) (Digital Versatile Disk+Recordable/Rewritable).
To enable copy-protection, a player or recorder for DVD/CD needs to distinguish between                read-only disks: DVD-Video, and        recordable/rewritable disks: DVD-R(W), DVD+R(W), DVD-RAM        
Though the pre-recorded content is encrypted (CSS, Content Scrambling System, or CPPM, Content Protection for Prerecorded Media), encryption alone does not offer a protection against bit-copies. Therefore, the player or recorder should refuse playback of encrypted content from recordable media. However, playback of encrypted content from read-only media must not be inhibited.
In order to distinguish recordable media from read-only media, the presence of a wobble is favorably detected, as recordable media have a pre-groove wobble while read-only media do not contain any wobble.
Before playback it is useful to distinguish between                CD, CD-R/RW and        DVD-ROM, DVD-R/RW, DVD+R/RW        
This can be achieved by analyzing the push-pull signal used for tracking, which is obtained by means of a proper combination of the four signals generated by four photodetectors of the optical pickup used for reading and/or recording. If the push-pull signal contains a wobble, the recording medium is recordable or rewritable. This is sufficient for determining the type of CD, but for DVD it is also important to distinguish between +R(W) and −R(W). If the wobble frequency for 1x speed is 817.5 kHz, the recording medium is +R(W). If the wobble frequency for 1x speed is 140 kHz, the recording medium is −R(W). The different wobble characteristics for different media are summarized in the following Table 1.
DVD + RWDVD − RWCD − RWchannel bit rate26.1626.164.3218(Mbit/s@1×)wobble frequency817.5140.6522.05(kHz@1×)channel bits per32186196wobble (Nw)wobble modulationBPSKAMFM bi-phase
As the ratio between the channel bit rate and the wobble frequency is constant, when the speed is not 1x the wobble frequency changes accordingly. The ratio is equal to the number of channel bits per wobble period, as listed in the table. The wobble signal and the data signal HF are fully synchronized, because they are obtained from the same four signals from the four photodetectors.
Before playback a wobble detector favorably provides the following information:                if the recording medium is a CD, it should determine whether there is the wobble or not,        if the recording medium is a DVD, it should determine whether there is a DVD+R(W) wobble or a DVD-R(W) wobble or no wobble.        